Condensation nuclei detector



June 5, 1962 .1.5. BlGELow ETAL 3,037,421

CONDENSATION NUCLEI DETECTOR l Filed July 27, 1956 2 Sheets-Sheet 1@ameri m Vis" /27 l/en'ons United States Patenti Oli-ice 3,037,421Patented June' 5, 1962 3,037,421 CONDENSATEN NUCLEI DETECTGER John E.Bigelow, Hales Corners, Wis., and Frank W. Van

Luik, Jr., and Stuart B. Dunham, Schenectady, and

Theodore A. Rich, Scotia, NX., assignors to General Electric Company, acorporation of New York Filed July 27, 1956, Ser. No. 660,540 '7 Claims.(Cl. 83-14) This invention relates to a method and apparatus formeasuring small particles, and more specilically those known ascondensation nuclei.

Condensation nuclei is a generic name given to small particles which arecharacterized by the tact that they serve as the nucleous on whichwater, for example, will condense to form droplet clouds. These nucleiare particles ranging in size from the sub-microscopic to themicroscopic. That is, the term condensation nuclei encompasses particlesfrom 2.5 10-8 :centimeter radius to 10-5 centimeter radius.

The nuclei serve as centers about which water droplets form and unlessthey `are present, no condensation will generally occur except atremarkable degrees of supersaturation. That is, it has been observedpreviously that the condensation of water vapor, or the like, does nottake place in the absence of such nuclei at values of supersaturationbelow 400%, a condition which normally does not occur.

The mechanism involved in the condensation of water vapor about suchnuclei is dependent both on the relative humidity and on the size of thenuclei. If the humidity of a gas or fair mass tends to rise above 100%,as would occur by a sudden cooling, condensation starts the depositionof water on the nuclei to achieve an equilibrium condition. Thedeposition of water will continue until the humidity is lowered to thenew equilibrium condition representing substantially 100% relativehumidity for the new temperature. The relationship between relativehumidity and particle size which controls the initiation of condensationon small particles or Adroplets is shown by the following table:

Size: Relative humidity, percent I cm. radius 350 l0"6 cm. radius 11210-5 cm. radius 101 l0"1 cm. radius 100.1

Condensation nuclei may be produced in many diverse ways. They may beeither nature produced or man-made. The primary source for natureproduced nuclei are volcanic eruptions, radioactive radiation, saltspray, evaporation of ocean water, atmospheric ionization and duststorms. The primary source of man-made condensation nuclei Iareco-mbustion processes and electromagnetic radiation.

As a consequence, the ability to measure the number of condensationnuclei in a very accurate fashion is extremely desirable in `order tostudy the various processes, both man-made and natural, which cause theproduction `of these condensation nuclei. That is, an laccu-1 rate meansfor measuring the concentrations of condensation nuclei would beextremely useful in meterological and atmospheric studies, air pollutionstudies, and investigations `of combustion processes. Thus it can beseen that `an urgent need exists for an accurate and sensitive means ofmeasuring condensation nuclei.

Due to the minute size of condensation nuclei great diiculty isencountered in their measurement since parti( cles lying in themicroscopic and sub-microscopic size ranges must be measured. As aresult, the usual techniques involving light absorption land lightscattering are of no utility since the condensation nuclei themselvesare small relative to the wave length fot visible light. As a result,there have been developed techniques for measuring condensation nucleiwhich rely on their property of acting -as the nucleus of a water drop.By causing condensation of water -about the nuclei, their size isincreased by many orders of magnitude so that the usual techniques maybe utilized in measuring.

The earliest device utilizing this approach for measuring condensationnuclei was the so-called Aitken counter. In this instrument, the airunder test is brought 'into a chamber lined with a wet blotter. Amanually operated piston expands and cools the =air thus raising therelative humidity above and causing water to condense about the nuclei.The water drops thus formed are deposited on a square glass slide andare counted with `a low power microscope. The Aitken counter, however,was and is an agonizingly ditlicult instrument to use. First, thecounting of the water droplets on the slide is an extremely tedious andlengthy operation. Furthermore, the instrument is extremely erratic inthat few consistent readings can be obtained. As a result it isnecessary to take the average of quite a number of readings in order tobe even vaguely certain of the results. Since it is necessary to take anaverage of several readings in order to obtain data which is even fairlyaccurate, this method is extremely time consuming and the device is mostunsatisfactory for measuring conditions in which the nucleiconcentration are varying `rapidly. Thus the inherent inaccuracy oftheAitken counter as well as its extremely slow response, makes it a mostunsatisfactory device to use.

Some of the major shortcomings of the Aitken counter are avoided by theNolan counter. in this device, the air sample is brought into a closedchamber which is traversed Vby a light beam. The air sample to bemeasured is pressurized by pumping in tiltered air. y en the pressurizedgas is allowed to come to atmospheric pressure by opening a valve in thechamber. The resultant expansion produces a fog lof water dropletscausing attenuation of the light beam traversing the chamber. Theattenuated light then provides an indication of the fog and,consequently, of the number of nuclei present. The Nolan counter solvedseveral of the dii'liculties presented by the Aitken counter in thatrapid and reproducible readings are ob-e tainable by means of thisdevice. However, the Nolan counter also has several seriousshortcomings. For all except very Ihigh concentrations of nuclei, theattenuation of light intensity in passing through the cloud formed inthe chamber is so small that, in order to obtain a measurable ndication,it is necessary to employ a very long chamber. Consequently, within therange of reasonable physical dimensions, the Nolan counter has asensitivity over only a very small range of condensation nucleiconcentrations. As a result, although the Nolan counter was asubstantial improvement over the Aitken device, it has only limitedutility due to its inherent lack of sensitivity.

Another significant prior art device for measuring condensation nuclei,which avoided some of the deficiencies of the Nolan and Aitken counters,is the Vonnegutcounter. 2,684,008 issued on July 20, 1954, to BernardVonnegut. In the Vonnegut apparatus the air or gas samples to be testedare brought to a 100% relative humidity by means of a humidifying devicesuch as a bubbler. The humiditied air samples are introduced into anexpansion chamber by means of a pressure sensitive llutter valve. Thehumidified air samples in the chamber are periodically expanded by meansof a flexible diaphragm which is cyclically driven by a `constant speedmotor. The movement of the bellows alternately expands and contracts thevolume ofthe chamber thus periodically expanding and cornpressing theair in the chamber.

During the outward displacement of the ilexible dia- The Vonnegutcounter is described in Patent No.-

phragm the air within the container is expanded and adiabatically cooledcausing supersaturation and in turn condensation of the water vaporabout the nuclei. The chamber is traversed by a beam of light which isscattered by the cloud of droplets within the chamber. The scatteredlight produces an electrical signal which is a measure of thecondensation nuclei present. In the latter part of the operating cycle,the exible diaphragm is inwardly displaced and in turn compresses theair in the chamber causing the droplets to be evaporated and expellingthe air sample through an exhaust conduit and a lter. The cycle ofoperation is then repeated to provide a continuous indication of thenumber of condensation nuclei present.

The Vonnegut apparatus provides solutions for a number of problems anddeiiciencies found in the Aitken and Nolan devices. Since scatteredlight rather than attenuated light is utilized to provide a measure ofthe number of condensation nuclei, a great increase in sensitiv-ity isachieved since, unlike the Nolan counter, it is possible to readrelatively low concentrations of nuclei. Furthermore, the device ofVonnegut operates continuously and consequently constitutes an automaticdevice for monitoring the condensation nuclei levels in a given area,whereas the Nolan device is manually operated.

Although the Vonnegut device has many advantages over the prior artdevices, it has certain limitations. In the Vonnegut 'device the air `isexpanded by means of a volume defined expansion inasmuch as the volumeof the chamber is varied by a piston, diaphragm, or such, moved in ageometrically dened manner. As a consequence, the speed of response isslow. That is, it is desirable that the ultimate degree ofsupersaturation be reached very quickly in order to prevent condensationfrom starting before the desired degree of supersaturation is reached.By utilizing a volume dened expansion the pressure drops slowly andcondensation begins almost immediately with its attendant release ofheat and reduction of relative humidity. Thus it is diicult to reach adesired degree of supersaturation and as a consequence it is difficultto tell precisely what expansion ratio is reached. As a result thereadings obtained may not provide t-he necessary degree of precisionwhere an extremely high degree of precision is desired.

Furthermore, since a flutter valve is utilized to admit the air samplesinto the expansion chamber, a certain ambiguity in the results may bepresent due to the fact that valves of this type are somewhat erratic asto the pressure at which they operate. Consequently, the operation ofthe valve does not necessarily introduce a sample of the same size intothe chamber with each operation. This presents certain ditliculties,since a device of this type has a detection sensitivity of the order ofone part by weight in 1014 part by weight of air, and any difference inthe size of sample pulled into the expansion chamber upon successivecycles could present a substantial error in the output readings.

Furthermore, the removal of prior air samples depend upon thecompression of the air sample in the chamber and consequent expulsionthrough an output conduit. This manner of expelling the previous sampleis somewhat imprecise since it is dilicult, in this fashion, to removethe prior sample completely from the chamber. As a result theindications may be somewhat ambiguous since it is unclear how much ofthe indication is due to the new sample and how much due to theremainder of the old sample. A further consequence of this manner ofexpelling the old sample, is that the apparatus has a slower responsethan is desirable since -it takes a substantial time to clear the priorcontamination out completely. That is, the Vonnegut device does not havea very precise ushing action, which permits the complete removal ofprior samples before a new sample to be tested is admitted to theexpansion chamber.

It is an object of this invention, therefore, to provide a condensationnuclei measuring apparatus and method which is extremely accurate andyet has very fast response. A further object of this invention is toprovide a condensation nuclei measuring apparatus in which the expansionratio ofthe tested samples is accurately controlled.

Yet another object of this invention is to provide a condensation nucleimeasuring apparatus in which the expansion of the tested samples ispressure defined.

Still another object of this invention is to provide a condensationnuclei measuring apparatus and method in which contamination of testsamples by previous samples is avoided.

Further objects and advantages will appear as the description of theinvention proceeds.

In accordance with the invention, a novel condensation nuclei measuringdevice is disclosed which has a very high order of accuracy and anextremely fast response time. The novel apparatus comprises an expansionchamber traversed by a beam of light which chamber is adapted to holdair or gas samples containing condensation nuclei. The input and outputconduits to the expansion chamber are controlled by a pair of rotaryvalve means which permit a controlled and very accurate operating cycle.The expansion of the sample in the chamber is achieved 4by a pressuredefined expansion, that is, a pressure difference is established betweenthe chamber and a source of infinite pressure, such as a pump. Theoutput valve operates to permit expansion of the gas sample periodicallyinto the source of lower pressure and a very rapid expansion of the gassample is achieved. Consequently, a very precisely `controlled level ofsupersaturation of the sample is possible and, consequently, a highlevel of accuracy may be achieved. *In addition, the rotary valves areso constructed that one portion of the cycle permits a thorough ushingof the expansion chamber so as to remove completely prior contaminatedsamples preventing any erroneous readings attributable thereto.

The novel yfeatures which are believed to be characteristic of thisinvention are set forth with particularity in the appended claims. Theinvention itself, however, both as to its organization and method ofoperation, together with further objects and advantages thereof, maybest be understood by reference to the following description taken inconnection with the accompanying drawing in which:

FIGURE l shows a view partially in cross section of the novel apparatusof the invention. t

FIGURE 2 is a fragmental perspective partially in cross section of theexpansion chamber and rotary valves of FIGURE 1.

FIGURE 3 is a perspective view of the valve rotor of FIGURE 2.

FIGURE 4 is a sectional View of the valve rotor taken along the line 4 4of FIGURE 3.

FIGURE 5 is another sectional view of the valve rotor taken along thelines 5-5 of FIGURE 3.

FIGURES 6a-6e are diagrams illustrating the relative position of thevalve during different portions of the operating cycle.

Referring now to FIGURE 1, there is shown an embodiment-of acondensation nuclei detecting apparatus illustrating the instantinvention. There is provided an elongated expansion chamber 1 into whichair samples are periodically introduced and expanded in order to formdroplet clouds. A beam of radiant energy is provided by an incandescentlamp 2, or any other similar source of radiant energy, positionedadjacent to one end of the expansion chamber 1. The beam of radiant energy from the incandescent lamp 2 traverses the expansion chamber 1 byvirtue of an optical system 3 mounted therein, shown in greater detailin FIGURE 2 and to be discussed later in connection therewith. Aradiation sensitive device 4, such as a photoelectric cell or aphotomultiplier device, is positioned adjacent to the other end of theexpansion chamber l and functions to intercept any light scattered inthe expansion chamber by the periodic format-ion of droplet cloudsWithin the chamber. The optical system within the chamber is so designedthat no light falls on the radiataion sensitive device 4 in the absenceof `a droplet cloud within the chamer. The precise manner in which thisis achieved will be discussed in detail later with reference to FIGURE2. Only upon the occurrence of such a cloud is light scattered withinthe chamber and caused to fall on the radiation sensitive device 4. Anyscattered light falling on the radiation sensitive device 4 functions toproduce a periodic electrical signal in its output which may beconnected to a measuring or recording instrument, not shown, in order toprovide a measure of the number of condensation nuclei present.

Additionally, there is provided a means for periodically expanding thecondensation nuclei containing samples in the chamber 1. To this end,there is provided a Valve means S consisting of a first valve portion Aand a second valve portion B. The valve means 5 is of the rotary typeand may be most clearly seen with reference to FGURES 2 and 3, andfunctions, broadly speaking, to control the periodic admission of gassamples into the expansion chamber l and the subsequent expansionthereof in order to produce droplet clouds. The rotary valve means 5, aswill be explained in greater detail later, consists of a boredcylindrical valve body and a rotor driven by a motor e. The rotor of thevalve means 5 has a number of recessed portions operative to perform thevalving function. Rotary valve means A is connected in an input conduit7 md periodically permits the introduction of yair samples into theexpansion chamber l. The rotary Valve means B is connected in an outputconduit 8 and operates to permit the periodic expansion of the gassamples in the chamber in order to form droplet clouds.

Also connected in the input conduit 7 is a humidifying element 9 whichfunctions to bring the samples to 100% relative humidity. The humidifier9 may be any one of many well-known types and may be a sealedcompartment having wicks dipped into a water container. Air passesdownward between the wicks on one side of a barrier, through a hole inthe barrier and back up the other side. In this fashion gas samplesbrought into this humidifier yare ybrought to 100% humidity. Other typesof humidiers may, of course,'be utilized. Thus, for example, if `desiredthe bubbler type of humidifier such as is shown in the Vonnegut patent,referred to above, may be utilized. It may also be desirable to positionthe humidifier 9 in close physical proximity to the expansion chamber lin order to avoid troublesome temperature differentials between thehumidifier and the expansion chamber.

The'output conduit 8 is connected to a pump 10 through a control valvelll and a water trap 13. The pump l provides an infinite source of lowerpressure and functions to expand the gas samples in the chamber 1through the valve means to a pressure determined by the control Valve1l, thus providing a rapid pressure defined expansion. T'ne controlvalve 1l is connected to the output conduit 8 and to an input line l2,and functions to limit the pressure differential applied to the samplesin the expansion chamber. The control valve permits air to bleed intothe pump line from the input line l2 if the pressure differentialreaches a preset value. This may be achieved by any number 4ofWell-known control valve means. For example, a spring force may bebalanced against the air pressure force from line l2 which is exertedagainst a washer. If the air pressure force is great enough, air flowsinto the pump line and reduces the pres- -sure differential. In thisfashion, a constant differential is maintained and a fixed degree ofexpansion of the gas samples in the chamber ll may be achieved. Inutilizing a pressure dened expansion of this type it is Vital that aconstant pressure differential be maintained since too low adifferential would not give the proper degree of expansion andsupersaturation required to cause condensation on small nuclei. On theother hand, too high a differential would cause either spontaneousvcondensation or condensation on charged molecules which causes thedesired signal to be masked. Furthermore, variations in the pressuredifferential would, of course, introduce ambiguities and errors intosuccessive readings. As a result, a control valve is desirable in orderto maintain the constant pressure differential.

The operation of the apparatus of FIGURE l is such as to permit aprecise and specified cycle of operations. Thesample to be tested entersthe humidifier 9 where it is brought to 100% relative humidity and tothe temperature of the chamber. This occurs during a portion of theoperational cycle denominated as the fiush portion. At this time, rotaryvalve A is open and valve B is partly open so the pump 10 can draw airright through the system in order to remove the previous sample as wellas to bring the new sample into the expansion chamber. The humidifiedair then passes through the valve A to the expansion chamber 1. Duringthe ll part of the cycle, valve B closes, stopping flow out of theexpansion chamber 1. Valve A, however, is still open so that aircontinues to flow in until inlet pressure is reached. The dwell part ofthe cycle then occurs in order to permit the gas sample in the expansionchamber to reach an equilibrium condition. That is, valve A closes andvalve B which has been closed previously remains closed allowing anoverlap in the valves.

During this dwell portion of the cycle, the gas sample in the expansionchamber is permitted to reach equilibrium conditions.

The next and final portion of the cycle is the expand portion duringwhich the gas sample is permitted to undergo a pressure definedexpansion in order to form a cloud of droplets about the condensationnuclei present in the sample. At the start of the expand part of thecycle, valve B opens fully and the pump 10 quickly pulls chamberpressure down to that determined by the pumplt) and the control valve11. The sudden expansion cools the air in the chamber. The amount ofwater vapor in the air which was of what could be retained at the formertemperature (i.e. 100% relative humidity) will be more than 100% of whatcan be retained `at the cooler temperature. Thus, Va condition ofsupersaturation exists instantaneously within the chamber. As a resultof the supersaturation, water vapor condenses on the condensation nucleito produce droplet clouds. The light passing through the cham# ber 1, isscattered bythe droplet cloud so that a portion of it reaches theradiation sensitive device 4 which is otherwise unilluminated.' As aresult, an electrical signal is produced in the output rof the radiationsensitive device 4 once per cycle. This electrical signal provides ameasure of the number of nuclei present, since the amount of scatteringof the light is dependent on the number'of nuclei about which dropletsare formed.

At the start of the next cycle, valve A reopens to initiate the flushcycle permitting complete removal of the previous sample. The pressurein the chamber goes back up,v and consequently the air temperaturetherein risesy and the droplets evaporate. Valve B is now only partiallyopen'and valve A is completed open so that the fiush portion of the nextcycle is initiated. The cycle described above may be repeatedapproximately 5 times per second, so that the output frequency of theradiation sensitive device 4 has a frequency of 5 cycles per second.That is, the motor 6 driving the rotor of the valve means 5 has al speedof 5 revolutions per second. It is obvious, of course, that the cyclefrequency just described is a matter of choice and that other cyclefrequencies may be utilized without departing from the spirit of theinstant invention.

As was pointed out with reference to FIGURE 1, the expansion chamber inconjunction with the rotary valve means constitutes the means by'whichsamples of gases are periodically drawn into the apparatus and caused toundergo an expansion in order to produce detectable droplet clouds.

FIGURE 2 illustrates, in detail, a preferred embodiment of an expansionchamber and rotary valve means which may be utilized in the apparatus ofFIGURE l. There is provided a cylindrical chamber 21 having a source ofradiant energy, such as the incandescent lamp 22, positioned next to oneend thereof. Mounted adjacent the other end of the chamber 21, is aradiation sensitive device 23 of the same type disclosed and describedwith reference to FIGURE l. The chamber 21 consists of two chamberportions 24 yand 25 separated by means of a divider` wall 26 having anelongated cylindrical passage 3i) therein. The chamber portion 25comprises the cloud forming chamber wherein the gas samples are causedto undergo expansion and form droplet clouds. An input conduit 37 and anoutput conduit 38 is provided for admitting the gas samples and forsubjecting `them to expansion by means of a pump such as illstrated inFIGURE l.

Mounted Within the chamber 21 is an optical system which functions toproject the beam of radiant energy through the chamber in such a mannerthat light falls on the radiation sensitive device only if a dropletcloud is present in the cloud chamber 25 to scatter light. A pair ofcondensing lenses 27 are positioned at one end of the chamber Z1 in athreaded lens mount 28. Thev condensing lenses 27 are positionedadjacent to the incandescent lamp 22 and function to focus the beam oflight to make an image thereof at the dividing barrier 26. A dividerlens 29 is positioned within the divider wall 26 and projects the beamof light which has been focused thereon through the cylindricalpassageway 30 and into the cloud forming chamber 2S. Since the lightfrom the incandescent source 22 is focused at the divider lens 29, thedivider lens acts effectively like a source at this point of thechamber. Thus, there is produced within the cloud chamber 25 a cone oflight subtending an angle a as shown in FIG- URE 2.

Positioned at the other end of the chamber 21 and adjacent to theradiation sensitive device 23 is a transparent window 31 positionedwithin a threaded mounting 32 and directly in front of the radiationsensitive' device 23. In order that only light scattered by dropletswithin the cloud chamber 25 impinge upon the radiation sensitive device23 and that none impinge thereon in the absence of droplets, an opaquelight carrier 33 of circular configuration is positioned in front of thewindow 31 in order to block any direct light path from the divider lens29. The light barrier 33 is fastened to the mounting member 32 by meansof struts 34 and 35.

In order to prevent stray light due `to multiple reiiections of theincoming ray from affecting the radiation sensitive device 23, theinterior surface of the cloud chamber 25 in the vicinity of the Window31 is threaded in order to absorb such reflected light by multiplereflections from the threaded portions. In addition, the end of thechamber 25 may be painted black or covered with black velvet in order tominimize further any stray reflected light.

If a cone of light subtending the angle a were projected toward thewindow 31 and its attendant light barrier 33, it is possible that someof the rays in this cone of light would strike the edge of the barrierand would be ditfracted towards the window 31 and would thus contributeto an erroneous and inaccurate reading. In order to avoid such apossibility, it is desirable to provide a cone of darkness subtending anangle b encompassing the light barrier 33 Within the cone of lightsubtending the angle a. To this end there is provided an opaque circulardisc 39 positioned on the face of one of the condensing lenses 27, Inthis fashion there is produced a cone of darkness within the cone oflight. The angle subtended by the cone of darkness being such that theedge of the light barrier 33 is kept dark. As a result,

only the light in the angular volume which is illuminated by rays inthe' cone of light and in the sight of the radiation sensitive device iselfective for producing a scattered light signal. This angular volume isillustrated in FIG- URE 2 by means of the dotted portion. As a result,the radiation sensitive device 23 intercepts a substantial portion ofthe light scattered by droplet clouds in the for- Ward direction. Inthis way a very sensitive means is provided for measuring the number ofdroplets within the cloud forming chamber 25.

A rotary valve means 40 is provided in order to control the admission ofgas samples into the cloud forming chamber 25 and the subsequentexpansion of the gas samples. The valve means 40 consists of a valvebody 4i having a cylindrical bored portion therein. The input conduit 37extends through the valve body 41 to form a first pair of ports 42extending into the bore and positioned at an angle of relative to eachother. The output conduit 33 similarly extends through the valve body 41into the bore to provide a second pair of ports 43 positioned at rightangles to each other. Positioned within the cylindrical bore of thevalve body 41 is a rotary member 44 fastened to a shaft 45 driven by amotor, not shown, such as is illustrated in FIGURE 1.

The rotor 44 has a circumferentially extending recessed portion which isalignable with the iirst pair of ports 42 upon rotation of the rotor 44.The recessed portion 46 permits the iiow of gas samples into the cloudchamber 25 through the input conduit 37 when the recessed portion 46 isin alignment with the ports 42. The recessed portion 46 is ofsubstantial width and, in a preferred embodiment, subtends an angle ofapproximately 225, as may be seen most clearly in FIGURE 4 which is asection taken along the line 4-4 of FIGURE 3.

Axially displaced from the recessed portion 46 is a second recessedportion, controlling llow through the output conduit 38, which permitsthe periodic expansion of the cloud samples within the cloud chamber 25.This second recessed portion consists of a relatively widecircumferentially extending recessed section 48 and a relatively narrowcircumferentially extending slotted section 47 connected thereto. As maybe seen most clearly with reference to FIGURE 5, which is a sectiontaken along the line 5--5 of FIGURE 3, the wide recessed portion 48, ina preferred embodiment, extends for an angle of approximately 90 whereasthe narrow slot portion 47 extends for approximately The recessedportions 46, 47 and 48 are so positioned around the circumference of therotor body 44 that they are simultaneously in alignment with theirrespective ports 42 and 43 during one portion of the cycle and out ofalignment during another. The relation of the recessed portions to theirrespective ports during different points in the operating cycle can bemost advantageously seen in FIGURES 6a-6e.

Referring now to FIGURES 6a-6e, there is illustrated, diagrammatically,the valve rotor positions relative to the ports 42 and 43 during variousstages of the operational cycle. 'Ihe left hand portion of each figureshows the relation of the rotor to the ports 42 in order to controlinput conduit 37 while the right portion shows its relation to ports 43and the output conduit 38. Referring specifical- 1y to FIGURE 6a, therotor position prior to the inception of a fresh cycle is illustrated.That is, the previous sample in the cloud forming chamber 25 has beenexpanded and a new cycle is about to begin. As can be seen fromreference to the left'hand portion of FIGURE 6a, the input conduit 37 isshutoff and no gas travels therethrough since the recessed portion 46 isnot in alignment with port members 42. The output conduit, on the otherhand, is open permitting expansion of air in the cloud chamber 25 sincethe recessed portions 48 and 47 are in alignment with the port members43.

Upon further rotation of the rotor member 44 the next portion of theoperating cycle, and more specifically, the flush portion of the nextcycle begins. FIGURE 6b shows the relative position of the rotor and theport members during the iirst portion of the new cycle during which theold sample is ilushed out of the cloud forming chamber 25 in order toremove the previously measured sample. IIhe input conduit 37 is now openpermitting new samples to be drawn into the cloud forming chamber. Thiscan be most clearly seen in the left hand portion of FIG- URE 6b sincethe recessed portion 46 has now come into alignment with the portmembers 42 permitting the tlow into the chamber. The output conduit 38similarly permits the flow of air therethrough since the recessedportions 48 and 47 are still in alignment With the ports 43. In thismanner the pump draws the old sample out of the cloud chamber Whilesimultaneously bringing in fresh samples Ithrough the input conduit 37.During the Hush portion, it can be seen that the ilow through the outputconduit 38 is limited in magnitude since the narrow recessed portion 47is in alignment with the ports 43 thus limiting the amount of ilow outof the chamber and preventing excess pressure differentials between theinlet and the chamber.

Upon further rotation of the rotor member 44, the next or ll portion ofthe cycle is initiated. As can be seen in FIGURE 6c, during the iillportion -of the cycle the input conduit 37 remains open permitting theflow of air into the cloud chamber since the recessed portion 46continues to remain in alignment with the ports 42. However, the outputconduit 33 has been shut off since the recessed portions 47 and 48 areno longer in complete alignment with the ports 43. As a result air nolonger flows out of the chamber, while air continues to ilow in throughthe inlet conduit 37 until the sample in the cloud chamber reaches inletpressure.

Following the fill portion of the cycle, the inlet conduit 37 is closedand the dwell portion of the operating cycle is initiated. The relativeposition of the rotors and the recessed portions can be most clearlyIseen in FIGURE 6d. In the left hand portion of FIGURE 6d it can be seenthat the recessed portion 46 is no longer in alignment with both ports42. As a result air or gas cannot flow therethrough and through theinput conduit 37 into the chamber. Similarly the output conduit remainsclosed preventing ilow out of the chamber. As can be s'een from theright hand portion of FIGURE 6d, the recessed portion 47 and 48 are alsonot in alignment with the port members 43. As a result the fresh samplein the chamber 25 is permitted to come to an equilibrium conditionbefore it is subjected to expansion.

Thes next portion of the operating cycle is the expand portion duringwhich the sample within the cloud chamber 25 is permitted to expand to alower pressure by means of a pump such as is illustrated in FIGURE l. Ascan be seen in FIGURE 6e the output conduit 38 is now opened since therecessed portion 48 has now come into alignment with the ports 43. Aswas pointed out previously, the recessed portion 48 is relatively largein magnitude thus permitting a very rapid ow and consequently a veryrapid reduction in pressure of the sample in the chamber. The inputconduit 37, however, still remains closed :since the recessed portion 46is as yet not in alignment With the ports 42 as may be clearly seen inthe left hand portion of FIGURE 6e.

The rapid expansion of the sample in the cloud chamber, as has beenpointed out previously, permits the condensation of water about thecondensation nuclei and causes the formation of a cloud of dropletsvtu'thin the chamber.

After the expansion of the sample as illustrated in FIG- URE 6e, thecycle repeats initiating with a flushing cycle which now removes thesample from the cloud chamber and introduces a new sample :as shown inFIGURE 6b. This permits a very precise control of .the expansion ratioof the sample as well as of its removal. As a result, a very accurateindication of the number of condensation nuclei present may be obtained.

Although a rotary valve embodying but a single rotor member havingseparate recessed portions is disclosed in order to control iiow throughthe input and output conduits, it is obvious, of course, that twoseparate rotary valves may be utilized without going outside of thespirit of the instant invention. Similarly although certainconiigurations of the recessed portion is illustrated, it is quitepossible to utilize congurations of many different types while stillfalling Within the Spirit of the instant invention.

While a particular embodiment of this invention has been shown it will,of course, be understood that it is not limited thereto since manymodifications both in the arrangement and in the instrumentalitiesemployed may be made. It is contemplated by the appended claims to coverany such modification-s as fall Within the true spirit and scope of thisinvention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In a condensation nuclei detecting apparatus, the combinationcomprising a chamber for holding humidiiied nuclei bearing gaseoussamples, said chamber having inlet and outlet conduits, means to expandsaid gaseous samples periodically to produce droplet clouds within saidchamber, said means including a iirst valve means disposed in said inletconduit to permit gas samples to be drawn into said chamber and secondvalve means disposed in said outletconduit to permit said gas samples tobe expanded, electro-optical means positioned to View the interior ofsaid chamber and measure the droplet cloud density as an index of thenuclei concentration, and means to operate said irst and second valvesin a predetermined sequence whereby samples are first drawn into saidchamber and then expanded to form said droplet cloud.

2. In a condensation nuclei detecting apparatus, the combinationcompirsing means defining a chamber for holding humidiiied nucleibearing gaseous samples, said chamber means having inlet and outletconduits communicating therewith, means to expand said gaseous samplesperiodically to produce droplet clouds within said chamber, said lastnamed means including a first rotary Valve means disposed in said inletconduit to permit samples to be drawn into said chamber and a secondrotary valve means disposed in said outlet conduit to permit samples insaid chamber to be expanded, common driving means for said first andsecond Valves to operate said Valves in a predetermined sequence wherebysamples are iirst drawn to said chamber and then expanded to formdroplet clouds, and electro-optical means positioned to View theinterior of said chamber and measure the density of said droplet cloudsas an index of the nuclei concentrations.

3. In a condensation nuclei detecting apparatus, the combinationcomprising means deiining a chamber for holding humidied nuclei bearinggaseous samples, inlet and outlet conduit means communicating with saidchamber, means to expand said gaseous samples periodically to producedroplet clouds within said chamber, said last named means including avalve means having a body portion containing a cylindrical bore, a iirstpair of ports extending into said bore and communicating with said inletconduit, a second pair of ports extending into said bore andcommunicating with said outlet conduit, a rotary member positionedWithin said bore having a iirst recessed portion alignable with said rstpair of ports to permit said samples to be drawn into said chamber, asecond recessed portion alignable with said second pair of ports topermit expansion of said gaseous samples in said chamber, said recessedportions being so positioned that during each rotation of said member avalving sequence is produced whereby gaseous samples are rst drawn intosaid chamber and then expanded to form said droplet clouds, andelectro-optical means positioned to view the interior of said chambercontinuously and measure the density of the droplet cloud as a measureof the number of nuclei.

4. In a condensation nuclei detecting apparatus, the combinationcomprising means dening a chamber for holding humiditied nuclei bearinggaseous samples, inlet and outlet conduits communicating with saidchamber, means to expand said gaseous samples periodically to producedroplet clouds within said chamber, said last named means including arotary valve means having a body with a cylindrical bore, axially spacedfirst and second pairs of ports extending into said bore andcommunicating respectively with the inlet and outlet conduits, a rotarymember mounted within said bore having axially spaced circumferentiallyrecessed portions sequentially alignable with rst and second pair ofports, means to rotate said rotary member to produce a valving sequencewhereby samples are rst drawn into said chamber and then expanded toform said droplet cloud, and electro-optical means positioned to viewthe interior of said chamber continuously and measure the density ofsaid droplet clouds as an index of the nuclei concentration.

5. In a condensation nuclei detecting apparatus, the combinationcomprising means defining a chamber for holding humidied nuclei bearinggaseous samples, an inlet conduit communicating with said chamber, anoutlet conduit communicating with said chamber, means to expand saidgaseous samples periodically to produce droplet clouds within saidchamber, said means including a valve body means having a cylindricalbore and a first pair of ports extending into said bore andcommunicating with said inlet conduit, a second pair of ports extendinginto said bore and communicating with said outlet conduit, a rotarymember mounted within said bore having a rst recessed portion alignablewith said trst pair of ports, and a second recessed portion including arestricted portion alignable with said second pair of ports, means todrive said rotary member to produce a valving sequence Whereby samplesare tirst drawn into said chamber, are expanded to form said dropletclouds and then caused to ow out of said chamber through said recessedportion and subsequently through said restricted portion on said rotarymember, and electro-optical means positioned to view the interior ofsaid chamber continuously and measure the droplet cloud density as aninlex of the nuclei concentration.

6. In a condensation nuclei detecting apparatus, the combinationcomprising a chamber having inlet and outlet means lfor holdinghumidiied nuclei containing gas samples, pump means connected to saidoutlet means to expand said samples, valve means in said inlet andoutlet means to permit samples to be drawn into said chamberperiodically and expanded periodically by said pump means to producecloud droplets about any nuclei, said valve means including a valve bodyhaving a cylindrical bored portion and a lirst pair of radial portsextending into said bored portion and connected to said inlet means, asecond pair of radial ports extending into said bored portion andconnected to said outlet means, a cylindrical rotary member mounted insaid bored portion having a first circumferentially extending recessedportion alignable with said trst pair of ports upon rotation of saidrotary member, and a second recessed portion including a restrictedportion alignable with said second pair of ports upon rotation of saidrotary member to permit expansion of said samples and to limit ow whensaid restricted portion is aligned with said second pair of ports, meansto produce a beam of radiant energy traversing said chamber which isperiodically scattered by said droplet clouds, radiation sensitive meansto intercept said scattered radiant energy to produce periodicelectrical signals as a measure of the number of nuclei present,

7. In a condensation nuclei detecting apparatus, the combinationcomprising a chamber adapted to hold humidied nuclei bearing gaseoussamples, said chamber having conduit means to permit the admission andremoval of said gaseous samples, means to expand said samplesperiodically to produce droplet clouds within said chamber including afirst positive valving means disposed in said conduit means to permitsaid samples to be drawn into said chamber and second positive valvingmeans disposed in said conduit means to permit said samples to beexpanded, means to operate said rst and second valving means in apredetermined sequence whereby samples are rst drawn into said chamberand then expanded to form said droplet clouds and means positionedadjacent to said chamber to measure the density of said droplet cloud asan index of the nuclei concentration.

References Cited in the tile of this patent UNITED STATES PATENTS1,608,812 Reeves Nov. 30, 1926 2,042,095 Grant May 26, 1936 2,118,836Carter May 31, 1938 FOREIGN PATENTS 406,648 Great Britain Feb. 26, 1934OTHER REFERENCES Cloud Chamber for Counting Nuclei in Aerosols, byBernard G. Saunders; The Review of Scientic Instruments, vol. 27, No. 5,May 1956, pages 273-277.

